Transmission Temp

[Ribtipram]

So what is the temp the cel comes on at.found this in another forum

 

[Texram155]

My 2010 stays at 155-170 with 95-100 degrees ambient temps. Now that we are in the 70-80’s it hangs out around 130

 

[Dusty]

Not really, as the coolant thermostat doesn't have much if any control over the trans temp. The trans cooler up by the radiator is air cooled not coolant cooled and the coolant is used for heating the trans fluid as much or more than for cooling it. The trans temp is controlled by a module on the trans that has it's own thermostat in the module. So if you are running a really cool temp thermostat, the thermostat in the trans module will just stay closed to get the trans fluid temp up. At least as far as I know.
I do know running a 190 stat in place of the 203 had no effect on trans temp on my 2016 hemi.

Pacofortacos is basically correct, but one point of clarification: at some point highly elevated transmission temperatures will be absorbed by the engine coolant.

From the 2019 Ram DT Service Manual

"This vehicle features an active transmission warm-up system with an oil-coolant heat exchanger on the transmission. The hoses are connected to the engine cooling system. The engine cooling circuit has both a three-way valve for coolant and a bypass valve in the transmission oil cooling circuit so the transmission oil can be warmed up more quickly from a cold start, which reduces parasitic loss from the drag of the spinning gears. If the transmission oil is getting too hot, such as during towing, the bypass valve setup directs oil from the heat exchanger and into the transmission cooler in the front-end cooling module."

Although in my experience the 8HP70 series rarely exceeds 200F in normal driving, and 210-215 under extreme limits, I would say that 245F is out of range for normal driving, especially when not towing over distance.

The question is will the 245F cause or be an indication of an internal transmission problem? The dealer is in a tough spot on this one because the factory will not reimburse under warranty unless something is visibly or functionally broken/inoperative, or there is a DTC set in the PCM.

There is a temperature sensor in the valvebody for measuring the transmission fluid temperature AND there is a setpoint in the PCM software to initiate a "Transmission Over Temperature" message. I am currently researching what the setpoint temperature is, but in the meantime it appears that it is not 245F , assuming everything in the system is operating correctly.

Best regards,
Dusty
2019 Ram DT 1500 Silver Billet Laramie, Quad Cab, 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, 18 inch wheels. Build date: 17 April 2018. Now at 023505 miles.

 

[JS4024]

Something is wrong, they are full of it being “normal”..... they have increased the temps to boost efficiency but your tranny is overheating. They left something disconnected or plugged up....check for a shop rag in the trans pan!

 

[Dusty]

If we assume that nothing in the transmission is causing excessive heat generation, then I would suspect a faulty bypass valve.

It would be worth verifying the transmission fluid level, although there's a DTC for low fluid, also. But I'm not sure how low it has to be to trigger the message.

2019 Ram DT 1500 Silver Billet Laramie, Quad Cab, 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, 18 inch wheels. Build date: 17 April 2018. Now at 023609 miles.

 

[Dusty]

If we assume that nothing in the transmission is causing excessive heat generation, then I would suspect a faulty bypass valve.

It would be worth verifying the transmission fluid level, although there's a DTC for low fluid, also. But I'm not sure how low it has to be to trigger the message.

2019 Ram DT 1500 Silver Billet Laramie, Quad Cab, 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, 18 inch wheels. Build date: 17 April 2018. Now at 023609 miles.

 

[pacofortacos]

Pacofortacos is basically correct, but one point of clarification: at some point highly elevated transmission temperatures will be absorbed by the engine coolant.

From the 2019 Ram DT Service Manual

"This vehicle features an active transmission warm-up system with an oil-coolant heat exchanger on the transmission. The hoses are connected to the engine cooling system. The engine cooling circuit has both a three-way valve for coolant and a bypass valve in the transmission oil cooling circuit so the transmission oil can be warmed up more quickly from a cold start, which reduces parasitic loss from the drag of the spinning gears. If the transmission oil is getting too hot, such as during towing, the bypass valve setup directs oil from the heat exchanger and into the transmission cooler in the front-end cooling module."

Although in my experience the 8HP70 series rarely exceeds 200F in normal driving, and 210-215 under extreme limits, I would say that 245F is out of range for normal driving, especially when not towing over distance.

The question is will the 245F cause or be an indication of an internal transmission problem? The dealer is in a tough spot on this one because the factory will not reimburse under warranty unless something is visibly or functionally broken/inoperative, or there is a DTC set in the PCM.

There is a temperature sensor in the valvebody for measuring the transmission fluid temperature AND there is a setpoint in the PCM software to initiate a "Transmission Over Temperature" message. I am currently researching what the setpoint temperature is, but in the meantime it appears that it is not 245F , assuming everything in the system is operating correctly.

Best regards,
Dusty
2019 Ram DT 1500 Silver Billet Laramie, Quad Cab, 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, 18 inch wheels. Build date: 17 April 2018. Now at 023505 miles.

Good info. I guess I could have been a bit clearer on the fact that the coolant can also cool it a bit. But the bulk of cooling is done via the transmission cooler on top of the AC condensor.

 

[pacofortacos]

If we assume that nothing in the transmission is causing excessive heat generation, then I would suspect a faulty bypass valve.

It would be worth verifying the transmission fluid level, although there's a DTC for low fluid, also. But I'm not sure how low it has to be to trigger the message.

2019 Ram DT 1500 Silver Billet Laramie, Quad Cab, 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, 18 inch wheels. Build date: 17 April 2018. Now at 023609 miles.

I would also lean that direction too. I wonder if the bypass valve is not redirecting the fluid up to the trans cooler.
Hopefully he doesn't have a plugged or kinked line going from the trans to the cooler.

I haven't looked but does the 8 speed have a check valve on the line up to the cooler like the older transmissions did???

 

[Dusty]

I would also lean that direction too. I wonder if the bypass valve is not redirecting the fluid up to the trans cooler.
Hopefully he doesn't have a plugged or kinked line going from the trans to the cooler.

I haven't looked but does the 8 speed have a check valve on the line up to the cooler like the older transmissions did???

I just researched the 2019 Ram DT service manual and I find no reference to it, either in transmission or fluid lines section. That doesn't mean it doesn't have one, however. The RFE series has the check valve built into the transmission, as opposed to the older RE series which had it in the cooling return line.

As an aside, the specifications for ATF+4 fluid indicate viscosity retention to over 350F. I suspect that the ZF fluid is as high or higher. Unfortunately in the time I have left this evening I haven't found a spec sheet for the ZF fluid.

Best regards,
Dusty
2019 Ram DT 1500 Silver Billet Laramie, Quad Cab, 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, 18 inch wheels. Build date: 17 April 2018. Now at 023609 miles.

 

[C Rogers]

I sympathize with you because of the issues you have had. With that said, can you imagine a world where dealers had to perform endless free services and replacements based "on what people read" on the internet?? They ALL would quickly go out of business. In this case, would 199 be OK but 201 is not because you "read it somewhere"? No, the system can't work that way.

So what to do? The manufactures have to "draw a line" somewhere to indicate where a real problem exists and work is warranted. They do that by having a CEL light up when some parameter is beyond a predetermined set point. They are not trying to burn you. You already got the trans replaced once. That was not free for them by any stretch. If this one is working, then it works.

I understand that they have to draw the line somewhere but when everyone that knows these vehicles says that's too hot I feel that they should at least take a look at it. I'm trying to get a jump on the problem if there is one. You're right, it's not free fore them to replace the tranny but it's not free for me either. For one thing, I don't have a vehicle to go back and forth to work to pay for this vehicle and it's a huge inconvenience. By trying to get them to at least take a look or hook up their own diagnostic machine to it, I'm trying to fix the problem so they don't have to replace another transmission. Saves them and me money and time.

 

[C Rogers]

So what is the temp the cel comes on at.found this in another forum

View attachment 183211

It's different every time. Some times it comes on at 185 others at 220.

 

[C Rogers]

On the 1500's can you purchase an aftermarket bypass like is available for the 66RFE & 68RFE? This dropped my temps by 25-30 degrees. Something just isn't right with the OP's set up. I personally would do whatever I could to rectify this situation. Written statements from accredited transmission shops, go to another dealer, contact "Ram Cares" on this forum. Do any or all of what I mentioned. That is NOT normal temps!

Took truck to my tranny guy and he hooked up his diagnostic machine, I drove the truck for 20 minutes, got it to 231 but his machine said 199. So he used the heat thermal camera on the tranny pan and lines and got a reading of 165 and 170. So trans fluid is not running hot but sensor may be faulty or there is an electrical issue going on. Just glad it's not really running as hot as the truck says it is. They still won't even look at it because no lights are on and they won't take my techs word on the issue. I will continue to drive it as they say it's safe until a light comes on. Fingers crossed that it never does.

 

[TomB 1269]

Took truck to my tranny guy and he hooked up his diagnostic machine, I drove the truck for 20 minutes, got it to 231 but his machine said 199. So he used the heat thermal camera on the tranny pan and lines and got a reading of 165 and 170. So trans fluid is not running hot but sensor may be faulty or there is an electrical issue going on. Just glad it's not really running as hot as the truck says it is. They still won't even look at it because no lights are on and they won't take my techs word on the issue. I will continue to drive it as they say it's safe until a light comes on. Fingers crossed that it never does.

BS
Go in with the report from the "tranny guy" and demand they replace the temp sensor in the tranny. Do not accept NO for an answer. The new transmission has a faulty sensor causing a high reading. I know I am not, and I am sure the service reps are not versed in exactly how the computer interprets that high of a temp reading, but I am sure that it has to be in a range in which the ECU starts to modify certain parameters. Does it start to delay shifts? Maintain torque converter lock mode longer, etc. in an attempt to manage fluid temperature?

Based on the information that has been stated here, there is at least one problem. That is the fact that the computer will change the tranny fluid flow to the cooler at to low a temperature for the "designed operation" of the ZF transmission, i.e. the bypass valve will open to soon, and at a minimum you will lose fuel efficiency. Worst the tranny could end up operating at too cold a temperature for the load on the truck during winter months.

Contact FCA as well and start a case........

 

[Dusty]

BS
Go in with the report from the "tranny guy" and demand they replace the temp sensor in the tranny. Do not accept NO for an answer. The new transmission has a faulty sensor causing a high reading. I know I am not, and I am sure the service reps are not versed in exactly how the computer interprets that high of a temp reading, but I am sure that it has to be in a range in which the ECU starts to modify certain parameters. Does it start to delay shifts? Maintain torque converter lock mode longer, etc. in an attempt to manage fluid temperature?

Based on the information that has been stated here, there is at least one problem. That is the fact that the computer will change the tranny fluid flow to the cooler at to low a temperature for the "designed operation" of the ZF transmission, i.e. the bypass valve will open to soon, and at a minimum you will lose fuel efficiency. Worst the tranny could end up operating at too cold a temperature for the load on the truck during winter months.

Contact FCA as well and start a case........

I agree with TomB, although I wouldn't go in to the dealer hot as a P-51 on a strafing run. I would think being proactive and saving FCA another $5K would be well received, if not by the dealer, at least by the factory.

The sensor is located in the valvebody which is spared and field replaceable, so the repair cost would not be that great.

Best regards,
Dusty
2019 Ram DT 1500 Silver Billet Laramie, Quad Cab, 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, 18 inch wheels. Build date: 17 April 2018. Now at 023898 miles.

 

[C Rogers]

Truck starting doing the hard downshift again every time truck comes to a complete stop. Every fix so far only last 5 weeks each time. First fix was new valve body (lasted 5 weeks) and then replaced entire transmission (lasted 5 weeks) I have reopened the case with FCA and have an appt. with service for Tuesday. I was told by service tech that replaced tranny that there's nothing they can do since they already replaced the tranny, he tried to convince me that this must just be a normal thing for this truck. I told him that's not normal and I have a friend who has the same truck, same year and same mileage and does not do this. I think they should replace the TCM which they only did an update for after the park assist recall and that's when the problem started.

 

[crash68]

I think they should replace the TCM which they only did an update for after the park assist recall and that's when the problem started.

The TCM for the 8 spd transmission is part of the valve body assembly(inside the transmission).

 

[C Rogers]

That's good to know I think. They tell me that they only update the TCM every time they do work on the transmission, they have never told me that they've changed it. The first time they did anything was they changed the valve body assembly and that worked for 5 weeks, then they changed the whole transmission, so they say, and that worked for exactly 5 weeks also. Is there a way for them to update the TCM or do they have to replace it when they replace the tranny? From my understanding they have not replaced the TCM, only thing they tell me is they do an update to the TCM. I don't know anything about transmissions so they could be blowing smoke up my ass for all I know. All I know is it's not normal to come to a stop and feel like you were hit from behind. Then weird thing is that when it happens the RPM's don't move and it never does it it tow mode. Something's wrong somewhere.

 

[hawsk99gt]

I am having the same exact issue with the over heating transmission. Had the transmission replaced 7 months ago at 65K. Now that I am at 81K and did a 1000k mile round trip from North Ga to Orlando Fla. At 70mph my transmission was reading 240 degrees. If I went up to 85mph it would jump up too 275 degrees and then I got a warning that flashed saying "I cannot maintain this temp mush longer". I had Dodge dealer check it out in Orlando last Friday and Saturday. They found no issue. They saw that I had a new Tranny installed and they said that they took it for a 10 mile ride but could not reproduce the issue. Mind you that the speed limit there is 65mph, so they did not go over that. Which where I live in GA, the top speed is only 55mph. And my dealer will not budge unless there is a code. I have about 15000k left on my warranty. I am going to attempt to get them to look at it with all the info I just read from you guys. But probably they will not do anything. The Orlando dealer was nice but said that they really could not do anything unless a code was thrown. I maybe SOL on this.

 

[Wild one]

I am having the same exact issue with the over heating transmission. Had the transmission replaced 7 months ago at 65K. Now that I am at 81K and did a 1000k mile round trip from North Ga to Orlando Fla. At 70mph my transmission was reading 240 degrees. If I went up to 85mph it would jump up too 275 degrees and then I got a warning that flashed saying "I cannot maintain this temp mush longer". I had Dodge dealer check it out in Orlando last Friday and Saturday. They found no issue. They saw that I had a new Tranny installed and they said that they took it for a 10 mile ride but could not reproduce the issue. Mind you that the speed limit there is 65mph, so they did not go over that. Which where I live in GA, the top speed is only 55mph. And my dealer will not budge unless there is a code. I have about 15000k left on my warranty. I am going to attempt to get them to look at it with all the info I just read from you guys. But probably they will not do anything. The Orlando dealer was nice but said that they really could not do anything unless a code was thrown. I maybe SOL on this.

The transmissions thermostat in the thermal management unit has been known to give trouble,and isn't usually changed when the transmission is changed.If you have a bad thermostat there's a good chance it was swapped onto your new transmission,so your over heating issue was never resolved.If you're up to try fixing it yourself,you could try one of Caulk04's thermostat bypass plugs.I think Jesse is only charging about 40 bucks for them with shipping.Takes about 20 minutes to install it,so you're not out a hell'va lot if it doesn't cure your issue. If they've changed transmissions,that would seem to rule out a bad temp sender unit,which kind of leads back to a bad thermostat in the thermal management unit ,it's part of that bigger looking aluminium heat exchanger bolted to the drivers side of the transmission,that pre-heats the transmission fluid.

 

[hawsk99gt]

Thanks for the input. Just got off the phone with my local service person from Dodge and I told him what I experienced. He definitely thought that temp was way too hot. He did look up what the normal temp was supposed to be and he said it should be around 195 to 210 of long highway driving. He told me he would pick his service managers brain about that and get back to me tomorrow. Told him about the info I got from here and the possible issues. I also mentioned I would hate to have to replace a whole transmission for something as simple as a thermostat issue. So we will see.